1. Field of the Invention
The present invention relates to a method for component verification during operation of a placement machine having a series of feeder slots for holding component feeders with feeder markers, each feeder marker associated with a component ID indicative of the type of component contained in the corresponding feeder, wherein each feeder slot has a slot ID, wherein said placement machine operates in correlation with a repeated sequence list with sequential steps, by which, upon receipt of a pick up trigger signal a feeder marker is scanned from the actual feeder in said actual feeder slot, while the machine is in progress of picking a component from said actual feeder, to determine the actual component ID associated with the feeder marker, the actual slot ID is determined, the intended component ID determined from stored configuration information, where the intended component ID is the ID of the type of component intended to be picked up from said actual feeder slot, the intended component ID is compared with the actual component ID and any discrepancy between the intended component ID and the actual component ID being indicated.
2. Description of Related Art
For electronic board assembly, automated component placement can reach very high speed up to tens of thousands of surface mounts of components per hour. These components are typically supplied by component vendors as rolled tapes of components that are loaded onto individual feeders which are mounted in corresponding feeder slots on the machine. These rolls of components may be loaded onto the feeders at a special loading unit, for example a stock room, after which the loaded feeders are placed in the feeder slots.
Component placement machines can have more than 100 feeder slots each accessible by a picking mechanism that picks individual components from the feeders in the slots and places them in particular predetermined locations on a printed circuit board. For application flexibility, each feeder and slot is generally constructed to be compatible with many different components.
The physical arrangement of components, feeders and slots must be in accordance with the expected arrangement as programmed in the machine. Any error in the arrangement can cause a corresponding error in the placement of components on the board. In a high volume, low mix manufacturing environment, a component loading error can produce a high number of defective printed circuit boards in a short period of time. In a low volume, high mix environment the chance of component loading error increases because of frequent feeder manipulation for product change over.
In order to eliminate loading errors, it is known to place bar code labels on individual feeders and slots for manual scanning to control that the rights components indeed are placed in the right slots according to predetermined configuration information, the so called a device list, which contains a listing of the slots and the components that are expected in the different slots. This procedure is carried out, before the machine begins its operation.
A different control system has been disclosed in U.S. Pat. No. 6,027,019. In this system, two scanners are adapted to monitor the arrangement of slot markers and feeder markers in the machine while the machine is in operation. The read slot marker and feeder marker are then compared with data in a device list.
In known machines, as for example indicated in U.S. Pat. No. 6,027,019, slot markers are far away from the corresponding feeder marker, which is due to constructional reasons. Therefore, two scanners are used and not just one single scanner that is able to scan both markers simultaneously.
In a production environment, those scanners may be exposed to dirt that may cover the reading unit resulting in an unsatisfactory control. Furthermore, the scanners are subject to risk of damage during machine maintenance or service. Therefore, it may be desirable to reduce the number of necessary scanners. Especially the slot scanner is subject to this risk in known machines.
Furthermore, a scanning of both the slot marker and the feeder marker implies that the component has to be picked up always at the same position, typically the central position, with respect to the slot. However, for some components, it is an advantage to pick up the component near to the edge of the feeder. This implies no problem for the feeder scanner, as the feeder marker may be at the pick up position of the feeder, but the slot reading cannot be performed properly in this kind of situations. For this reason it may be desirable to avoid the slot marker scanner.
To avoid installation of a slot marker scanner, a system for commercially available placement machines has been constructed where a detector counts the number of rotations of a spindle used to displace the slots in front of the component pick-up. This way, the actual count in the detector is associated with the actual slot. Simultaneously, the feeder marker is scanned in order to verify that the slot and the component in the feeder of that slot are in accordance with the associated device list. Such a system is commercially available from the company named Surpass Technologies Limited.
For this kind of counters, regular calibration is necessary, because drift in the mechanical system of the counter may lead to malfunction. Also, in case of electric failure, the counter needs calibration before being ready to operate. Conventional calibration of the control mechanism needs stopping of the operation of the complete machine and translation of the slot table to a position well defined for the counter. Stopping of the machine, however, is not desirable. This kind of system is not well suited for feeders, which have a non-centered pickup position.